Wireless communication is made between a plurality of wireless communication devices. In such wireless communication, a demand for spectrum has increased. In order to address a problem of lacking spectra, there has been proposed a technique for dynamic spectrum access (DSA). An exemplary technique for dynamic spectrum access is cognitive radio (see Patent Document 1, for example).
In a cognitive wireless communication system, at first, a spectrum sensor scans a wireless frequency environment. A result of the spectrum sensing is transferred, as an output, to a cognitive engine (CE) which is also called the brain of the cognitive wireless communication system. Then, the cognitive engine (CE) analyzes sensing information. A frequency band (frequency opportunity) available in the cognitive wireless communication is specified based on the analysis.
In the cognitive wireless communication system, a local analysis may be preliminarily made in the spectrum sensor, and in this case, obtained information is transferred to the cognitive engine (CE) to be used for a final determination.
As described above, in the cognitive wireless communication system, the sensing information is obtained as a result of the spectrum sensing thereby to enable the cognitive wireless communication.
Herein, if spectra can be rapidly sensed (or the obtained sensing information can be rapidly exchanged), the obtained spectrum opportunity is expected to be able to be immediately used. However, on the other hand, in the cognitive wireless communication system, reliability of the spectrum sensing needs to be enhanced for protecting a licensed wireless communication service. In other words, if reliable spectrum sensing can be rapidly performed within a limited period of time, a communication efficiency of the cognitive wireless communication can be expected to be enhanced.
The present inventors have invented a spectrum sensor having both a communication function (transmission/reception function) and a spectrum sensing function (which will be called dual spectrum sensor below) (Non-Patent Document 1). However, in such a dual spectrum sensor, with one output, the communication function needs to be stopped for sensing spectra to save a time for sensing spectra.
From the above, in the cognitive wireless communication, it was not easy to meet both reliability of the spectrum sensing and rapid spectrum sensing (or rapid communication after the spectrum sensing). When a time for sensing spectra is previously defined depending on the standard specification and when a time for the communication function cannot be secured while a time for communication is previously defined depending on the standard specification, a time for sensing spectra cannot be secured. Thus, the communication efficiency of the spectrum cognitive wireless communication was difficult to further enhance.